(1) Field of the Invention
This invention relates to a paper sizing agent. More particularly, the invention relates to an internal paper sizing agent which is excellent in sizing effect and which can be employed in the range of neutral to alkali without using conventional fixing agents such as aluminum sulfate.
(2) Description of the Prior Art
In the paper manufacturing industry, the sizing agents that are prepared from natural rosins or modified rosins, especially fortified rosin sizing agents that are prepared by saponifying maleic-modified rosins, are regarded as most preferable ones and are widely used. These sizing agents are used together with aluminum sulfate and fixed to paper fibers in an acidic region of pH 4.0 to 5.0. Owing to the acidic condition with using these sizing agents, the following disadvantages are caused to occur. That is, paper making machinery suffers from corrosion, strength and durability of obtained paper are lowered, and inexpensive alkaline fillers such as calcium carbonate cannot be used because alkaline fillers are decomposed.
For this reason, neutral sizing agents which can be fixed to wood pulp without using aluminum sulfate, are proposed. For example, a sizing agent is known in which alkyl retene dimer is dispersed in water in the presence of cationic starch. This is, however, defective in that the cost is high and it takes much time to produce desired sizing effect.
Furthermore, several inventions have been proposed with regard to neutral sizing agents.
In U.S. Pat. No. 3,102,064, a sizing agent represented by the following general formula is disclosed. ##STR1## in which R represents a dimethylene or trimethylene radical and R' is a hydrophobic group containing more than 5 carbon atoms and is selected from the class consisting of alkyl, alkenyl, aralkyl, and aralkenyl groups.
Proposed in British Patent No. 2,015,612 are "substituted succinic anhydrides having substituent groups of butene oligomers having 16 to 40 carbon atoms". The compounds disclosed in both the above patent specifications are, however, unsatisfactory in sizing effect.
In U.S. Pat. No. 3,821,069, a reactive sizing agent is disclosed. The sizing agent is produced by reacting maleic anhydride and an internal olefin corresponding the following general structure: EQU R.sub.x --CH.sub.2 --CH.dbd.CH--CH.sub.2 --R.sub.y
and the reaction product is represented by the following general formula: ##STR2## wherein R.sub.x and R.sub.y are, respectively, alkyl radicals containing at least 4 to 10 carbon atoms.
In Japanese Laid-Open Patent Publication No. 57-154,495 is proposed a reactive sizing agent which consists of an alkenyl succinic anhydride mixture that is produced by adding maleic anhydride to a mixture of straight chain internal olefins having 8 to 18 carbon atoms and double bonds which are almost evenly distributed to each position except .alpha.-position.
These sizing agents are high in reactivity with paper fiber and produce good sizing effect. However, they are liable to be hydrolyzed and they must be used as soon as possible after being emulsified. In addition, as the sizing effect varies widely, constant and uniform sizing effect cannot be expected in paper sizing operation.